The present invention relates to a device for measuring the fluid consumption of a user over a given measurement time of the type comprising a meter arranged upstream of the user connection point, which meter is designed to measure a quantity of fluid delivered to the user during a space of time under consideration, and, connected to said meter, an information processing unit including means of evaluating the quantity of fluid measured by said meter.
It is known practice for users to be provided with a nitrogen-production unit in order to meet their requirements for fluid.
This unit is rated to supply a nominal flow rate required by the user. This nominal flow rate is determined from a predicted estimate of the instantaneous consumptions. However, the user""s requirement for gas may vary over time, and in particular may exhibit spikes in the consumption.
To constantly satisfy the user""s requirements, the production unit conventionally includes a gas production machine associated, in parallel, with a gas storage tank. Thus, during peak consumption time, when the machine alone is unable to supply the gas required, gas is drawn from the storage tank.
The storage tank is generally replenished periodically, for example using a tanker truck.
The cost prices of the gas produced by the production machine and of the gas from the storage tank are different. It is thus permissible for the gas supplier, who owns the installation, to invoice the user at different rates for the gas from the production machine and for the gas from the storage tank, the rate applied to the gas from the tank being higher than the rate applied to the gab produced by the machine.
For this reason, the gas production installation has two volumetric meters, one of them arranged immediately at the outlet of the gas production machine and the other arranged immediately at the outlet of the storage tank.
These meters are read periodically, for example every month, and the quantities of gas read off each meter are charged at the corresponding rate.
The device for measuring the consumption is not fully satisfactory as it assumes that the gas production machine is capable of constantly maintaining a stable flow rate equal to the nominal flow rate agreed with the user.
Thus, in practice, if the performance of the machine is below the nominal performance, a high quantity of gas is taken from the storage tank, and this results in an increase in cost to the user.
By contrast, if the machine performance is better than the required performance, recourse to the storage tank is raze, which means that the flow rate does not reflect the user""s increase in consumption.
Likewise, in the event of a succession of significant fluctuations in the actual flow rate of the machine about the nominal flow rate, the quantity of gas extracted from the storage tank bears no relation to the phases in which the user exceeds its nominal flow rate. Thus, the volumes measured by the sensors do not correspond to the service actually provided to the user.
The object of the invention is to provide a device for measuring the consumption of fluid which does not have the disadvantages mentioned hereinabove and which, in a simple way, allows the quantities consumed by the user and corresponding to flow rates higher than a determined nominal flow rate to be determined accurately.
To this end, the subject of the invention is a device for measuring the fluid consumption by a user over a given time, at the aforementioned type, characterized in that said information processing unit includes:
means for storing at least one nominal consumption threshold in memory;
means of reading the meter during said given time at successive moments so as to determine the quantity of fluid delivered to the user over each interval defined between two successive moments;
means of comparing, across each interval, measured quantities with at least one reference value which represents the or each nominal threshold across the interval under consideration;
means of summing, across all of the intervals covering said measurement time, the amounts by which each measured quantity exceeds the or each reference value for the interval under consideration; and
means of summing, across all the intervals covering said measurement time, that portion of each measured quantity that is below the or each reference value for the interval under consideration.
According to particular embodiments, the measurement device includes one or more of the following features:
the duration of each interval is shorter than the mean period of the fluctuations of the user""s consumption over time about the nominal consumption threshold;
the durations of all the intervals of said measurement time are equal; and
the meter is designed to measure the volume of fluid consumed, and the or each reference value for each interval is equal to the volume of fluid which should be consumed during the interval under consideration for consumption that corresponds to the or each nominal consumption threshold.
Another subject of the invention is the application of such a device to the supply of a gas, particularly a gas or gaseous mixture separated from the air.